Integrated Optical Receivers for Telecommunications: A Critical Discussion

The impressive development of first generation optical fiber communication systems has been mainly based on the progress in the technology of fibers and sources. Even though some amount of work has been devoted to the receiver optimization, it mainly concerned the electronic circuitry, that is the optimization of the processing of the signal after the photoelectric conversion. Without exception, in all the systems in use today, the carrier is intensity modulated and direct detection is accomplished at the receiver. The widespread use of direct detection in fiber systems is due to different reasons: the spatial multimode structure of the field to be detected, the lack of stable and spectrally pure sources, the simplicity and in many cases satisfactory properties of the direct detectors. In recent years, however, due to the general development of the field pushing toward the exploitation of better performances of the systems in terms of bandwidths and distances, and given the availability of single-mode fibers and stable single-frequency lasers, new attention has been paid to the possible alternatives for detection, namely quantum amplifiers and heterodyne receivers.